This invention relates to a carbon fiber and, more particularly, to a process for producing a pitch carbon fiber bundle adjusted in the form of a coil.
In general, carbon fibers are roughly divided into a PAN system and a pitch system. PAN carbon fibers are produced by firing polyacrylonitrile fiber under specific conditions. Pitch carbon fibers are produced by melt spinning an anisotropic pitch or isotropic pitch and thereafter infusibilizing and carbonizing it.
These carbon fibers are applied to products adapted for features depending upon raw materials and characteristics and widely utilized as materials for aerospace industry, sports or leisure products.
The carbon fibers which have heretofore been produced have excellent physical and chemical properties such as light-weight, high strength, heat resistance and chemical resistance. However, the carbon fibers generally exhibit a behavior as brittle materials and have low elongation and inferior softness. Accordingly, the prior art carbon fibers are not necessarily suitable as materials for which these characteristics are required. Further, in the prior art process for producing carbon fibers, it is difficult to produce fibers or fiber bundles having excellent elongation and elasticity.
In view of such prior art, we have already proposed a process for producing a curl-shaped fiber comprising an isotropic texture and an anisotropic texture and having excellent elasticity by separately feeding an isotropic pitch and an anisotropic pitch and spinning these pitches from a spinneret at the same time (Japanese Patent Laid-Open Publication No. 90626/1991).
According to this process, carbon fiber materials having excellent elasticity can be obtained with relatively low cost. However, the softening point of the isotropic pitch is different from that of the anisotropic pitch and their attenuation behaviors after discharge are different. Accordingly, it is not necessarily easy to spin the isotropic and anisotropic pitches at the same time. Further, in the case where the isotropic and anisotropic textures only coexist or coexisted these fibers are merely infusibilized and carbonized, the resulting fibers are randomly curled every single yarn and therefore bulky and wavy fibers are obtained, but fibers having good stretchability cannot be obtained. Thus the fibers are not entirely satisfactory.